Generally, a semiconductor processing apparatus that uses a vacuum load lock system includes a load lock chamber, a transfer chamber and multiple reaction chambers that are connected to the transfer chamber. For each apparatus, a substrate-handling robot is used to automatically supply substrates to the reaction chambers. In such an arrangement, an atmospheric robot first brings a substrate inside the load lock chamber from a cassette or a front opening unified pod (“FOUP”). The FOUP may comprise a detachable cassette and a box with a front-opening interface. After the substrates are placed in the load lock chamber, the load lock chamber is evacuated, and the substrate is transferred to a reaction chamber by a vacuum robot provided inside a common polygon-shaped transfer chamber. After the substrate is fully processed in the reaction chamber, it is returned to the load lock chamber by the vacuum robot. Lastly, after the load lock chamber is restored to atmospheric pressure, the processed substrate returned to the cassette or the FOUP by the atmospheric robot. This type of apparatus is generally called a “cluster tool.”
As the number of reaction chambers increases, the area occupied by the processing apparatus (the “footprint”) and the width of the front panel of the apparatus (the “faceprint”) increase, as does the cost of operation. This is because the conventional single-wafer processing apparatus possesses a common polygon-shaped transfer chamber to which each of the reaction chambers is attached, radiating in all directions. Additionally, the number of reaction chambers in a layout is limited by the number of sides of the polygon-shaped transfer chamber. Furthermore, in the conventional single-wafer processing apparatus, each reaction chamber has independent gas and vacuum lines, and each reaction chamber independently performs deposition (film forming). Thus, if the number of reaction chambers is to be increased to improve productivity, the number of gas lines and vacuum pumps must increase as well, thereby increasing the complexity of the processing apparatus.
To reduce the footprint or the faceprint of the conventional single-wafer processing apparatus, a transfer mechanism has been included inside the load lock chamber. The transfer mechanism is simply a handling unit capable of holding substrates and loading/unloading substrates from the reaction chamber. The load lock chamber is separated from the reaction chamber using a gate valve. This configuration allows the footprint or faceprint of the processing apparatus to be reduced to a certain degree, but the reduction is not satisfactory, no improvement of process efficiency or productivity is made, and the total system is generally not simplified. Furthermore, this configuration makes it difficult to supply wafers to the reaction chambers in a continuous chemical vapor deposition (“CVD”) process, such as in an ashing process. Finally, during deposition a film is apt to form around the gate valve, thereby necessitating installation of an expensive plasma-proof O-ring for CVD processes using plasma.
Although incorporation of a W-shaped transfer arm into the load lock chamber may solve some of these problems, so doing increases the capacity of the load lock chamber, thereby increasing the time required for evacuating and pressurizing the load lock chamber and thus decreasing processing capacity.